If you need to update every record in a file using another value from the same record, SQL would be a good option. If this is a one-off exercise, then SQL will be ideal. If this is something that’s going to happen more often I would suggest writing a program for it (you could also use embedded SQL if you want).
Use the STRSQL command to start an interactive SQL session.
First use the SELECT command to check whether your statement will give you the expected results :-
(e.g. need to add postage to total price)
SELECT product_code, (total_price + postage), total_price, postage FROM product_file
IF your happy with the results, then you can use the UPDATE command :-
UPDATE product_file SET total_price = (total_price + postage)
This will then update the field total_price with the curent value of total_price + postage.
Hope this helps.